Device and method for detecting snow and ice

Abstract

A device for detecting snow and ice which has a humidity sensor and an ambient temperature sensor. An evaluator switch is controlled according to a humidity sensor-measured variable, producing a control signal at set humidity values for defrosting a surface which is being monitored for snow and ice. The ambient temperature sensor activates the humidity sensor within a temperature range of between +2° C. and −12° C. The humidity sensor itself has a PTC (positive temperature coefficient) heating element. The current consumption of the heating element is used as a measure of humidity. Both the ambient temperature sensor and the humidity sensor are positioned at a mutual distance in a longitudinally extended sensor cartridge made of plastic. The temperature sensor is thermally decoupled from the PTC heating element. The PTC heating element is built into a metal sleeve in such a way that it is corrosion and humidity proof.

What is claimed is:  
     
       1. Device for detecting snow and ice including a humidity sensor mounted in a peripheral environment for determining a humidity in a surrounding atmosphere subject to exposure by any of a snow precipitation, an ice formation and a water-vapor containing air with which a heating current circuit is associated, and an evaluation circuit controlled in dependence on a humidity sensor-measured variable, which produces a switching and/or control signal at predetermined humidity values, characterized in that an ambient temperature sensor is arranged in a control circuit which activates the humidity sensor when a temperature within a predetermined temperature range is detected; that the humidity sensor has a PTC (Positive Temperature Coefficient) resistance or heating element whose operating state with an electrical current consumption changes depending upon an ambient temperature change and an energy dissipation loss to said environment and atmosphere, which electrical current consumption is monitored by an electrical measuring current circuit and is used as an indicator of the humidity; and that the two sensors are mutually spaced within an elongate sensor cartridge such that the temperature sensor is thermally decoupled from the PTC heating element. 
     
     
       2. Device as claimed in claim  1 , characterised in that the sensor cartridge is constructed in the form of a plastic tube, arranged on one end of which there is a cable entry and in whose opposite end region the PTC heating element is arranged in a metal or glass sleeve. 
     
     
       3. Device as claimed in claim  2 , characterised in that the temperature sensor is arranged within the plastic tube near to the cable entry and remote from the PTC heating element. 
     
     
       4. Device as claimed in one of claims  1  to  3 , characterised in that the control circuit controls a switch which closes the measuring current circuit of the humidity sensor. 
     
     
       5. Device as claimed in one of claims  1  to  3 , characterised in that a current consumer with a threshold value setter is associated with the measuring current circuit and when the current consumption of the PTC heating element exceeds the threshold value the switching and/or control signal may be triggered. 
     
     
       6. Device as claimed in claim  5 , characterised in that connected after the current consumer there is an adjustable time setter which holds the switching and/or control signal for a preset period of time. 
     
     
       7. Device as claimed in claim  1 , characterised in that the switching and/or control signal controls a heating device for thawing purposes, by way of a switch, which is preferably constructed as a load relay, and/or warning device. 
     
     
       8. Device as claimed in claim  1 , characterised in that the control circuit additionally activates a lead time suppresser which suppresses the release of the switching and/or control signal for a predetermined period of time until the PTC heating element has reached a steady operational state. 
     
     
       9. Device as claimed in claim  1 , characterised in that the ambient temperature sensor with an associated output circuit is used to monitor a device response temperature alert zone, which said temperature sensor with said output circuit has means for adjusting an upper and/or lower threshold temperature and that the humidity sensor may be activated when the temperature falls below an upper threshold value. 
     
     
       10. Device as claimed in one of claims  1  to  9 , characterised in that visual indicating means are coupled to an output of at least the control circuit and the evaluation circuit. 
     
     
       11. Device as claimed in claim  10 , characterised in that visual indicating means are additionally coupled to an operating current source and to a heater controller. 
     
     
       12. Method for detecting snow and ice using a device as claimed in claim  1 , characterised in that a humidity sensor including a PTC heating element, an electrical heating current circuit and an ambient temperature sensor are arranged mutually spaced and thermally decoupled in an elongate sensor cartridge, that is connected to receive electrical power from a mains voltage and an operating current source, while the sensor cartridge is immersed in a monitored zone at risk of snow and ice, whereby the ambient temperature sensor detects the ambient temperature, that the electrical heating current circuit of the PTC heating element is activated in dependence on the temperature falling below a preset threshold value; and that a measured drawn current in the heating current circuit of the PTC humidity sensor is sensed and a switching and/or control signal is triggered when the electrical current exceeds a predetermined threshold value. 
     
     
       13. Method as claimed in claim  12 , characterised in that a temperature window is set between +5° C. and −20° C. and the heating current circuit of the PTC heating element is activated only within this window. 
     
     
       14. Method as claimed in claim  12  or  13 , characterised in that a heating device in the form of a surface heater, which heats a roof, one or more roof gutters and/or one or more parabolic mirrors, or a warning signal is activated with the switching and/or control signal. 
     
     
       15. Method as claimed in claim  14 , characterised in that a minimum activation time of the surface heater is preset. 
     
     
       16. Method as claimed in claim  1 , characterised in that the electrical current flowing through the PTC heating element is measured and the switching and/or control signal is triggered, when the humidity sensor is activated, in dependence on making a comparison of whether said current flowing through said PTC heating elements exceeds a current strength threshold value. 
     
     
       17. Method as claimed in claim  1 , characterised in that when the temperature falls below an upper threshold value a lead time suppresser is triggered with which the output of the switching and/or control signal is suppressed for a predetermined time until the temperature or current consumption of the PTC heating element is able to reach an operational equilibrium in a steady state. 
     
     
       18. Method as claimed in claim  1 , characterised in that a set of operational states of the ambient temperature sensor and/or the humidity sensor and/or a heater and/or a lead time suppressor and the presence of the mains voltage are indicated visually to either a local or remote observer.